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Thread: Bad gas mileage with new spark plugs

  1. #1
    Join Date
    Feb 2003
    Location
    Kansas
    Posts
    263
    My Cars
    99 M3 etc...

    Bad gas mileage with new spark plugs

    I have been driving around this weekend with new spark plugs. The same driving condition I always drive.

    My average with the new plugs is about 24.5 mpg. I was getting about 30.5 mpg with the old ones around town.

    The only thing I can think of is that they do not have the correct gap. I bought factory replacement plugs from the dealer. They told me I did not need adjust the gap, just take them out of the box and put them in.

    I should have just left the original 95,000 plugs in my car. They seem to perform better. Any ideas why the new ones dont work as well?

  2. #2
    Join Date
    Aug 2002
    Location
    Northern VA
    Posts
    185
    My Cars
    1993 318i
    Which plugs did you get? What model and year is your car?

    Most plugs need to be gapped, except for a few (like the Bosch +4s).
    1993 BMW 318i
    4-cylinder 1.8L MTX
    127,000 miles
    4-door (Color: Cashmere)

    Replaced air flow meter boot (cracked), spark plugs, rear shock mounts (left side busted) & shocks, driver-side plastic window sliding pieces (broken 2x), 02 sensor, exhaust support bracket/shackle (rusted through), and thermostat

  3. #3
    Join Date
    Feb 2003
    Location
    Kansas
    Posts
    263
    My Cars
    99 M3 etc...
    I got the Bosch platinum plugs for my 1995 318ti.

    I figured they would need to be gaped but the dealer told me just to take them out of the box and put them in. I think they maybe pulling my leg. Are they full of B.S.?

  4. #4
    Join Date
    Aug 2002
    Location
    Northern VA
    Posts
    185
    My Cars
    1993 318i
    The dealer is correct.

    If you have either the Bosch Platinum+4s or Bosch Platinum+2s, then they don't need to be gapped.

    Are you getting any misfiring?

    You might want to recheck the torque on the plugs, and that the plug wire boots are on the plugs tight.

    I used to run with the +4s, but I switched to normal double platinum plugs, since I heard that some people have problems with the Bosch plugs.
    1993 BMW 318i
    4-cylinder 1.8L MTX
    127,000 miles
    4-door (Color: Cashmere)

    Replaced air flow meter boot (cracked), spark plugs, rear shock mounts (left side busted) & shocks, driver-side plastic window sliding pieces (broken 2x), 02 sensor, exhaust support bracket/shackle (rusted through), and thermostat

  5. #5
    Join Date
    Jul 2002
    Location
    Knoxville, TN
    Posts
    2,693
    My Cars
    '04 M3/MT Coupe,'04 X3
    I would double-check to make sure the plugs are in all the way (torque) and that they're getting spark (the wire is on or the coil is seated...whatever you've got).

    I'd also double-check to make sure that the spark-plugs are the right one for the car. I've had places give me the wrong plugs on a number of occasions.
    -Aaron
    2004 M3 - Coupe, 6spd, Silver Grey on Black
    | RAC RG63, PSS, ZCP Brakes, aFe, SS (V1, Res. X-pipe, Street Muffler), Epic Alpha-N, 319whp |
    2006 Jetta TDI/DSG, Pkg 2, Silver on Black - Sold
    2004 M3 SMG - Silver Grey on Black, Convertible - RIP
    1995 525I 5spd - Black on Black -Sold
    2004 X3 3.0i AT- Blue on Tan - For the wife....

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